It looks like either your router does not support uPnP or natPmP or those services are turned off in your router. If possible, you could try to enable uPnP in your router and see where that gets you.
If uPnP does not work, then you need to setup port forwarding manually.
Use of both uPnP and manual port forwarding are explained in the Roon Help Centre article at:
Hello again,
Thx for respons. After resetting my network, trying to fix the loosing audi endpoint problem, I had some difficulties to connect ARC again. But all good.
Now I only have to wait to see how long I keep my audio endpoint before it’s lost again.
This network has multiple NAT layers, so port forwarding will be vulnerable to port conflicts or firmware resets between multiple routers (not to mention ISP implementation).
Since your ROCK machine appears to be a UEFI-based model, you might find the RoonOS Tailscale interface to be a simpler solution than port forwarding.